Rats exchange goods and services using human tit-for-tat rules

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Wow. And wow. Exciting findings from a new scientific study indicates the intelligence of rats extends to using the same rules as humans for exchanging goods and services.

Norway rats trade different commodities

Researchers have shown for the first time in an experiment that non-human animals also exchange different kinds of favors. Humans commonly trade different commodities, which is considered a core competence of human species. However, this capacity is not exclusively human as Norway rats exchange different commodities, too. They strictly follow the principle “tit for tat” — even when paying with different currencies, such as grooming or food provisioning.

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Backstory

Although a high level of cooperation is our trademark, cooperation is not uniquely human. Many animals help each other, too, like bees managing their hive. Human cooperation often follows the reciprocal strategy “I help you because you helped me before.” Such reciprocal cooperation has been claimed to be cognitively demanding, especially when different commodities are exchanged.

Trading of different commodities is a fundamental component of human interactions, enabling for instance division of labour, which is the basis of our ecological and economic success. It has been argued that the high cognitive demands of such trading may hamper cooperation in non-human animals. In contrast, several studies of wild animals have suggested an exchange of different commodities, but hitherto this has not been examined by controlled manipulations of the behavior of test subjects.

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The study

In an experimental study, researchers from the Institute of Ecology and Evolution of the University of Bern tested whether common Norway rats engage in reciprocal trading of two different forms of help, i.e. allogrooming and food provisioning. Their test rats experienced a partner either cooperating or non-cooperating in one of the two commodities. To induce allogrooming, the researchers applied saltwater on the test rats’ neck, which is hardly accessible to self-grooming, so help by a partner is needed.

To induce food provisioning, partner rats could pull food items towards the test rats. Afterwards, test rats had the opportunity to reciprocate favors by the alternative service, i.e. allogrooming the partner after receiving food from it, or donating food after having been allogroomed.

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The results

The test rats groomed more often cooperating than non-cooperating food providers, and they donated food more often to partners that had heavily groomed them before. Apparently, they traded these two services among another according to the decision rules of direct reciprocity.